In a silicon single crystal, a crystal defect size tends to be reduced when an oxygen concentration is reduced. For example, in a silicon single crystal wafer obtained by slicing a silicon single crystal of low oxygen concentration, such as a silicon single crystal in which an initial interstitial oxygen concentration is 8 ppma or lower, in particular, 5 ppma or lower, it is difficult to detect micro crystal defects such as a BMD (Bulk Micro Defect), a COP (Crystal Originated Particle), and a “void”, which makes it extremely difficult to make a judgment about a defect region as to whether a silicon single crystal wafer obtained by slicing is a defect-free region or not.
For a crystal defect that is difficult to detect due to a minute size thereof, a method for detecting such a crystal defect by making the crystal defect apparent has been known.
For example, in Patent Literature 1, a method for evaluating a silicon wafer, the method for evaluating a silicon wafer wherein heat treatment that grows oxygen precipitates without generating new oxygen precipitates is performed on a silicon wafer containing oxygen precipitates that are smaller than the lower limit size of an oxygen precipitate that can be detected by a particular measuring apparatus in order to grow all the oxygen precipitates that are smaller than the lower limit size to a size that can be detected by the particular measuring apparatus and then an oxygen precipitate density in the silicon wafer is measured by the particular measuring apparatus is described.
Moreover, in Patent Literature 2, a method for revealing crystal defects in bulk silicon substrate, the method that performs heat treatment called “revealing heat treatment” that is conducted in a non-reducing atmosphere at a temperature in the range from 500° C. to 1300° C., is described. Specifically, the “revealing heat treatment” is performed in an atmosphere of oxygen, argon, nitrogen, or a mixture of two of them.